Table system and method for pet/ct imaging

ABSTRACT

The present disclosure provides a table and an imaging system and method for PET/CT imaging. The table may include a base, a bracket, and a plate movable relative to the bracket. The bracket may include a releasing position, a CT scan position, and a PET scan position. The table may extend the scan range of the CT scanner without changing the size of the imaging system.

The application is a continuation of U.S. patent application Ser. No.15/281,577, filed on Sep. 30, 2016, now U.S. Pat. No. 10,568,596, whichclaims priority of Chinese Patent Application No. 201610498791.4 filedon Jun. 30, 2016, and Chinese Patent Application No. 201610498768.5filed on Jun. 30, 2016, the entire contents of each of which are herebyincorporated by reference.

TECHNICAL FIELD

This application generally relates to medical diagnosis, andspecifically, relates to a table system and method for PET/CT imaging.

BACKGROUND

With the advance of science and technology, medical imaging has obtainedgreat development, and more imaging modes have become available, such asX-Ray photography, magnetic resonance imaging (MRI), computed tomography(CT), positron emission tomography (PET) and so on, each of which withits strengths may complement each other.

PET is a fairly advanced clinical imaging technique in the field ofnuclear medicine. In PET, a positron generated by the decay of aradionuclide gets in collision with a negatron in vivo, then thepositron and the negatron are annihilated with each other, two gammaphotons are emitted in almost opposite directions. Functionalinformation relating to metabolic activities may be obtained by way ofdetectable gamma rays to diagnose a disease. A PET image may show thefunctional information and identify a tumor. However, the resolution ofthe PET image may be low.

CT is another clinical imaging technique in which a specific part of abody with a certain thickness may be scanned. For instance, when X rayspass through human tissues, a portion of the X rays may be absorbed bythe tissues, and a portion passing through the body may be detected by adetector on the basis of which a corresponding signal may be generated.Corresponding to the differences in densities of various tissues and thedifferences in the x-ray penetration abilities, the detected rays may bedifferent. The signal corresponding to the detected rays may beconverted to a digital signal. The digital signal may be processed by acomputer, and then an image may be generated and displayed. A minorlesion in vivo may be identified based on the image. The CT may generatean anatomical image with a high resolution and a high sensitivity inidentifying the morphology of a tissue. However, CT may lack thecapacity to determine other characteristics of the lesion.

PET/CT is a technology combining CT with PET. It may provide theinformation of CT and PET with only one diagnostic examination using asame table and a same image processing workstation. Fused images may beobtained by image reconstruction and image fusion. The fused images mayshow both functional and anatomical information. The fused images withmore complementary information and higher resolution may improvediagnostic accuracy. For instance, the fused images may provide moreinformation for making a treatment plan for tumor.

A PET/CT fused image may be obtained by superimposing one image onanother of a same anatomical location or level. In this case, thevertical position of the table on which a patient may be placed forexamination may need to be controlled to facilitate the image fusion.

Usually, a plate of the table supported at only one end may be displacedrelative to the CT scanner in an axial direction during a CT scanning.When the plate extends out, because of the weight of a patient placed onthe plate, the plate may bend within a scanning cross-section. Thescanning cross-section may be a plane perpendicular to the rotation axisand through an iso-center of the CT scanner. The plate may also bendduring a PET scanning. The CT image and the PET image at a sameanatomical location or level may need to be matched so that the CT imageand the PET image may be fused. Hence, the bending of the plate may needto be corrected in order to match a CT image with a corresponding PETimage.

Besides, in the PET/CT system as illustrated in FIG. 1(a), a table unit13 includes a base 133, a bracket 132 and a plate 131. Plate 131 maymove relatively to the bracket 132 along the axial direction. There is aposition 1331 for a CT scan (shown as a dotted line in FIG. 1(a)) and aposition 1332 for a PET scan (shown as a dotted line in FIG. 1(a)) onthe base 133 along the z axis parallel to the rotation axis of the CTscanner 11 (i.e., the length direction of the plate 131). When thebracket 132 is placed at position 1331 for a CT scan, a patient may beplaced onto or removed from the table unit 13 (e.g., the plate 131 ofthe table unit 13). The plate 131 may exit from the bore of CT scanner11 completely to avoid collision with CT scanner 11 when the plate 131is moved up or down. In this case, the distance between one end of theplate 131 close to CT scanner 11 and the scanning cross-section islarge. CT scan may not be performed before the plate 131 arrives at thescanning cross-section. In the case of a fixed maximum moving distanceof the plate 131, the further an initial position of the plate 131 isaway from the scanning cross-section, the smaller the scanning range ofCT scanner 11 is.

SUMMARY

A first aspect of the present disclosure relates to a table. The tablemay include a base, a bracket, and a plate. The plate may be configuredto move relatively to the bracket. There may be various positions on thebase along a length direction of the plate including a position at whicha patient may be placed onto or removed from the table (or referred toas a releasing position), a position for CT scan (or referred to as a CTscan position), and a position for PET scan (or referred to as a PETscan position). When the bracket is placed at the releasing position,the position of the plate is adjustable (e.g., by moving the plate up ordown) and the distance between the floor and the plate may be in therange from 450 mm to 1000 mm, from 500 mm to 1000 mm, from 550 mm to 950mm, or from 550 mm to 945 mm. When the bracket is placed at the CT scanposition, the position of the plate is adjustable (e.g., by moving theplate up or down) and the distance between the floor and the plate maybe in the range from 700 mm to 1000 mm, from 750 mm to 1000 mm, from 800mm to 950 mm, or from 820 mm to 945 mm. The plate is movable (e.g., bymoving the plate up or down) for a first distance from the floor whenthe bracket is placed at the PET scan position of the base and the plateis movable (e.g., by moving the plate up or down) for a second distancefrom the floor when the bracket is placed at the CT scan position,wherein the first distance is the same as the second distance.

A second aspect of the present disclosure relates to a PET/CT system.The PET/CT system may include a CT scanner configured to perform CTscanning, a PET scanner configured to perform PET scanning, and a tableunit. The table unit may include a base, a bracket, and a plate. Theplate may be configured to move relatively to the bracket. There is areleasing position, a CT scan position, and a PET scan position on thebase of the table unit. When the bracket is placed at the releasingposition, the position of the plate is adjustable (e.g., by moving theplate up or down) and the distance between the floor and the plate maybe in a range from 450 mm to 1000 mm, from 500 mm to 1000 mm, from 550mm to 950 mm, or from 550 mm to 945 mm. When the bracket is placed atthe CT scan position, the position of the plate is adjustable (e.g., bymoving the plate up or down) and the distance between the floor and theplate may be in a range from 700 mm to 1000 mm, from 750 mm to 1000 mm,from 800 mm to 950 mm, or from 820 mm to 945 mm. The plate is movable(e.g., by moving the plate up or down) for a first distance from thefloor when the bracket is placed at the PET scan position of the baseand the plate is movable (e.g., by moving the plate up or down) for asecond distance from the floor when the bracket is placed at the CT scanposition, wherein the first distance is the same as the second distance.A maximum scan range of the CT scanner may be from 1700 mm to 2100 mm,2060 mm, 2000 mm, 1960 mm, or 1900 mm. The PET scanner may achieve awhole body scan with one scan. A field of view of the PET scanner may befrom 1700 mm to 2000 mm, from 1800 to 2000 mm, or from 1900 mm to 2000mm.

In some embodiments, the PET/CT system may further include a measuringunit and a height adjustment unit. The measuring unit may be configuredto measure the distance of the plate from the floor (or referred to asthe height of the plate) at the scanning cross-section during the CTscanning. The height adjustment unit may be configured to adjust theheight of the plate according to the height of the plate measured by themeasuring unit during the CT scanning.

In some embodiments, the PET/CT system may further include an obtainingunit configured to obtain images, a determining unit configured todetermine a relationship between the heights of the plate from a floorin the images and the distances of the plate moving along the lengthdirection of the plate (or referred to as the axial direction), and aheight adjustment unit configured to adjust the height of the plateaccording to the relationship such that the movement (including, forexample, the movement along the length direction, the height adjustment,and the bending) of the adjusted plate fitting the relationship. Theimages may be CT images or topograms. In some embodiments, therelationship may be linear or essentially linear. In some embodiments,the relationship may be non-linear.

In some embodiments, the PET/CT system may further include a correctingunit configured to correct a position error of the plate during the PETscanning compared to the CT scanning.

In some embodiments, the PET/CT system may further include a correctingunit configured to correct data acquired in the PET scanning.

A third aspect of the present disclosure relates to a method for PET/CTimaging. The method may include loading a patient when the bracket isplaced at a releasing position, performing a CT scan when the bracket isplaced at the position for CT scan and performing a PET scan when thebracket is placed at the position for PET scan.

In some embodiments, the method may include adjusting a first height ofthe plate from the floor according to a second height of the plate fromthe floor at the scanning cross-section during the CT scanning so that achanging trend of the first height of the adjusted plate from the flooris consistent with a changing trend of the second height of the platefrom the floor during the CT scanning. In some embodiments, theadjustment may be made before performing a PET scan.

In some embodiments, the method may include obtaining CT images ortopograms, determining the relationship between the heights of the platefrom the floor in the CT images or topograms and the distances of theplate moving in the length direction of the plate, and adjusting theplate according to the relationship to make the movement of the adjustedplate fitting the relationship. In some embodiments, the relationshipmay be linear or essentially linear.

In some embodiments, the method may include correcting the PET dataafter performing a PET scan.

Additional features will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the artupon examination of the following and the accompanying drawings or maybe learned by production or operation of the examples. The features ofthe present disclosure may be realized and attained by practice or useof various aspects of the methodologies, instrumentalities andcombinations set forth in the detailed examples discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further described in terms of exemplaryembodiments. These exemplary embodiments are described in detail withreference to the drawings. The drawings are not to scale. Theseembodiments are non-limiting exemplary embodiments, in which likereference numerals represent similar structures throughout the severalviews of the drawings, and wherein:

FIG. 1(a) is a diagram of a prior art PET/CT system in which a CT scanis being performed;

FIG. 1(b) is a diagram illustrating the bending of the plate of a tablein a CT scan;

FIG. 2(a) is a diagram of a prior art PET/CT system in which a PET scanis being performed;

FIG. 2(b) is a diagram illustrating the bending of the plate of a tablein a PET scan;

FIG. 3 illustrates an exemplary PET/CT system according to someembodiments of the present disclosure;

FIG. 4 is a diagram illustrating an exemplary PET/CT system according tosome embodiments of the present disclosure;

FIG. 5 is a diagram illustrating an exemplary PET/CT system according tosome embodiments of the present disclosure;

FIG. 6(a) is a diagram illustrating an exemplary PET/CT system accordingto some embodiments of the present disclosure;

FIG. 6(b) is a diagram illustrating a CT scan performed by the PET/CTsystem illustrated in FIG. 6(a);

FIG. 6(c) is a diagram illustrating a PET scan performed by the PET/CTsystem illustrated in FIG. 6(a);

FIG. 7 is a flowchart illustrating an imaging method according to someembodiments of the present disclosure; and

FIG. 8 is a flowchart illustrating another imaging method according tosome embodiments of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant disclosure. However, it should be apparent to those skilledin the art that the present disclosure may be practiced without suchdetails. In other instances, well known methods, procedures, systems,components, and/or circuitry have been described at a relativelyhigh-level, without detail, in order to avoid unnecessarily obscuringaspects of the present disclosure. Various modifications to thedisclosed embodiments will be readily apparent to those skilled in theart, and the general principles defined herein may be applied to otherembodiments and applications without departing from the spirit and scopeof the present disclosure. Thus, the present disclosure is not limitedto the embodiments shown, but to be accorded the widest scope consistentwith the claims.

It will be understood that the term “system,” “unit,” “module,” and/or“block” used herein are one method to distinguish different components,elements, parts, section or assembly of different level in ascendingorder. However, the terms may be displaced by other expression if theymay achieve the same purpose.

It will be understood that when a unit, engine, module or block isreferred to as being “on,” “connected to” or “coupled to” another unit,engine, module, or block, it may be directly on, connected or coupledto, or communicate with the other unit, engine, module, or block, or anintervening unit, engine, module, or block may be present, unless thecontext clearly indicates otherwise. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

The terminology used herein is for the purposes of describing particularexamples and embodiments only, and is not intended to be limiting. Asused herein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include,”and/or “comprise,” when used in this disclosure, specify the presence ofintegers, devices, behaviors, stated features, steps, elements,operations, and/or components, but do not exclude the presence oraddition of one or more other integers, devices, behaviors, features,steps, elements, operations, components, and/or groups thereof.

In an imaging system or a method according to the present disclosure, arelationship between the heights of the plate from a floor and thedistances of the plate moving in an axial direction (or a lengthdirection) of the plate is determined from images in advance. The platemay be adjusted so that the movement of the plate (including, forexample, the movement along the axial direction, the height adjustment,and the bending of the plate) may conform to the relationship. At thispoint, an image of a patient may be obtained. Scan data may be correctedaccording to the position error between a height of the plate from thefloor in previously acquired images and a height of the plate from thefloor during imaging. The previously acquired images and the currentimages may be matched to facilitate image fusion. The imaging system ormethod according to the present disclosure may compensate a differenceof the bending of the plate between different imaging modes.Consequently, the image matching or fusion may be simplified and thequality of image fusion may be improved. The system in the presentdisclosure may be CT, MRI, PET or any combination thereof. In thefollowing embodiments of the present disclosure, a PET/CT systemcombining CT with PET described below is merely provided forillustration purposes, and not intended to limit the scope of thepresent disclosure.

FIG. 1(a) is a diagram of a prior art PET/CT system in which a CT scanis being performed; FIG. 1(b) is a diagram illustrating the bending ofthe plate of a table in a CT scan; FIG. 2(a) is a diagram of a prior artPET/CT system in which a PET scan is being performed; FIG. 2(b) is adiagram illustrating the bending of the plate of a table in a PET scan.

With reference to FIG. 1(a), a PET/CT system may include a CT scanner11, a PET scanner 12, and a table unit 13. The CT scanner 11 may beconfigured to run a CT scan and the PET scanner 12 may be configured torun a PET scan. The table unit 13 may include a base 133, a bracket 132and a plate 131. The plate 131 may be configured to move relatively tothe bracket 132 in an axial direction. There may be a position 1331 forCT scan (shown as dotted line) and a position 1332 for PET scan (shownas dotted line) on the base 133 along z axis which is parallel to arotation axis of the CT scanner 11 (i.e., length direction of the plate131). The bracket 132 at position 1331 may be used for CT scan, and thebracket 132 at position 1332 may be used for PET scan. The table 131 maybe configured to support and transport the patient from a region to beimaged to a scanning cross-section of CT scanner 11 or a field of view(FOV) of PET scanner 12. Wherein the scanning cross-section is a planeperpendicular to the rotation axis and through an iso-center of the CTscanner 11. Usually, the distance between position 1331 and position1332 along z axis may be equal to the distance between the iso-center ofthe CT scanner 11 and the center of FOV of the PET scanner 12.

As shown in FIG. 1(a), during the CT scanning, the bracket 132 may beplaced at position 1331, and the plate 131 supporting the patient movesalong the positive direction of the z axis t, and transfer the region tobe imaged (e.g., head of the patient) to the scanning cross-section ofthe CT scanner 11. An x-ray tube of the CT scanner 11 may be configuredto emit radiation rays and a detector of the CT scanner 11 may beconfigured to detect radiation rays traverses the region to be imaged.And then a reconstruction unit may be configured to reconstruct CTimages based on a processed detected signal.

During the CT scanning, the plate 131 may bend when moving towards theCT scanner 11 because of the weight of the patient and/or the weight ofthe plate itself. The further the plate 131 extends out, the more theplate 131 may bend. For different positions of the plate 131 at thescanning cross-section, the height of the plate 131 at the scanningcross-section may be different. The height of the plate 131 may be thedistance between the plate 131 and the floor on which the table (e.g.,the base of the table) is placed. In the CT images so acquired, thebending of the plate 131 may increase along an inverse direction of thez axis, as shown in FIG. 1(b). Please note that the bending of the plate131 shown in FIG. 1(b) is exaggerated for illustration purposes.

As shown in FIG. 2(a), during a PET scanning, the bracket 132 atposition 1332 and the plate 131 may operate in concert to transfer theregion to be imaged of the patient to the FOV of the PET scanner 12. Theplate 131 may bend due to the weight of the patient and/or the weight ofthe plate 131 itself. During a PET scanning, the plate 131 may bestationary. In the PET images so acquired, the bending of the plate 131may increase along a positive direction of the z axis, as shown in FIG.2(b). Please note that the bending of the plate 131 shown in FIG. 2(b)is exaggerated for illustration purposes.

Comparing CT images in FIG. 1(b) with PET images in FIG. 2(b), thetrends of the bending of the plate 131 in these two imaging modes aredifferent. Because the distance between position 1331 and position 1332is equal to the distance between the iso-center of the CT scanner 11 andthe center of FOV of the PET scanner 12, the bending of the plate 131 ator around the portion corresponding to the middle of the region to beimaged in a CT image may be approximately equal to the bending of plate131 in a corresponding PET image. The bending of other portions of theplate 131 in the CT image may be different from the bending of the platein the corresponding PET image.

As described in background, for PET/CT, an image showing both functionaland anatomical information may be obtained by fusing a CT image and aPET image.

To improve the accuracy of fused images, an imaging system in someembodiments of the present disclosure may compensate a difference in thebending of the plate 131 between different imaging modes. With referenceto FIG. 3, a diagram illustrating an exemplary PET/CT system accordingto some embodiments of the present disclosure. The PET/CT system 30 mayinclude a CT scanner 31, a PET scanner 32, and a table unit 33. In someembodiments, the CT scanner 31 and the PET scanner 32 may be coaxial. Insome embodiments, the CT scanner 31 and the PET scanner 32 may benon-coaxial. The table unit 33 may include a base 333, a bracket 332,and a plate 331. The plate 331 may be configured to move relatively tothe bracket 332 along a length direction of the plate 331. There is aposition 3331 for CT scan (indicated by a dotted line) and a position3332 for PET scan (indicated by a dotted line) on the base 333 along thez axis. The z direction may be parallel to the rotation axis of the CTscanner 31 (also the length direction of the plate 331). When thebracket 332 placed at position 3331, a CT scan may be performed. Whenthe bracket 332 placed at position 3332, a PET scan may be performed.The plate 331 may be configured to support and/or transport the patientso that the region to be imaged may be moved to the scanningcross-section of the CT scanner 31 or a field of view (FOV) of the PETscanner 32. As used herein, the scanning cross-section is a planethrough the iso-center and perpendicular to the rotation axis of the CTscanner 31. There is a height adjustment unit 34 on one side of the PETscanner 32 away from the CT scanner 31. By adjusting the plate 331according to the height of the plate 331 at the scanning cross-sectionduring the CT scanning, a changing trend of the height of the plate 331during the CT scanning may be reproduced or mimicked.

To control the height adjustment unit 34 to drive the plate 331 and tocompensate a difference in the bending of the plate 331 between the CTimaging mode and the PET imaging mode, the PET/CT system 30 may furtherinclude an obtaining unit 35 and a determining unit 36.

The obtaining unit 35 may be configured to obtain images. In FIG. 3, theobtaining unit 35 may be connected to the CT scanner 31. In someembodiments, the obtaining unit 35 may acquire a CT image, instead of CTscan data. The CT scan data may be sent to a data acquisition unit andthen reconstructed in an image reconstruction unit to generate the CTimage provided to the obtaining unit 35. In some embodiments, obtainingCT images is merely provided for illustration purposes, and not intendedto limit the scope of the present disclosure. As used herein, CT imagesmay be computed tomographic images.

In some embodiments, the images obtained by the obtaining unit 35 may betopograms. As used herein, a topogram may be a photograph acquired bysetting the radiation source at a certain projection angle. In someembodiments, CT images and topograms may be obtained through the CT unit31 of the PET/CT system 30, or through one or more stand-alone CTapparatuses. In some embodiments, the CT images or topograms may beimages retrieved from a storage.

The determining unit 36 may be configured to determine a relationshipbetween the heights of the plate in the images (e.g., CT images,topograms, etc.) and the distances of the plate moving in the axialdirection of the plate.

In some embodiments, a coordinate system may have its origin set at theiso-center of the CT scanner 31. Every pixel in a CT image may have acoordinate value. A minimal coordinate value in the x axis of the pixelscorresponding to the plate 331 of CT images may be designated as alowest point of the plate 331. The coordinate value in the x axis of thelowest point may represent a height of the plate 331. The height of theplate 331 may be the distance of the plate 331 from the floor on whichthe table unit 33 is placed. Thus, the height of the plate 331 in a CTimage may be obtained by analyzing CT images. Coordinate values of theother pixels may be selected to represent the height of the plate 331.The height of the plate 331 of CT images may be obtained by other means.For example, a measuring unit may measure the height of the plate 331when the different portions of the plate 331 pass through the scanningcross-section. As another example, a distance measuring unit may measurethe distance along the x axis between the portion of the plate 331 atthe scanning cross-section and the distance measuring unit. The distancemeasuring unit may be a sonar or a laser rangefinder. Other devices thatmay measure the height of the plate 331 are within the scope of presentdisclosure.

During the CT scanning, a displacement of the plate 331 along the z axismay be recorded. According to the height of the plate 331 in CT imagesand the displacement of the plate 331, a relationship between theheights and the displacements of the plate 331 may be determined. Insome embodiments, the relationship between the heights and thedisplacements of the plate 331 may be approximately linear. In someembodiments, the relationship between the heights and the displacementsof the plate 331 may be determined by linear fitting. The displacementsof the plate 331 may be the same as or relate to the distances of theplate moving in the axial direction. The shorter the scanning range is,the closer to being linear the relationship between the bending or theheights and the displacement of the plate 331 may be. In someembodiments, the gradient of the linear relationship may be the ratio ofa change in the bending to the corresponding change in the displacementof the plate 331 based on a geometric relationship. For example, theratio of the maximum change in the bending to the maximum relativedisplacement of the plate 331 may be calculated to obtain the gradientof the linear relationship. As used herein, the maximum change in thebending of the plate 331 may refer to the maximum difference between theheight of a first portion of the plate 331 in a first CT image and theheight of a second portion of the plate 331 in a last CT image. As usedherein, the maximum relative displacement may refer to the differencebetween the position of the plate 331 in the z axis corresponding to thefirst CT image and the position of the plate 331 in the z axiscorresponding to the last CT image. The gradient of the linearrelationship may be symbolized by a parameter k. In some embodiments,the linear relationship may be symbolized by one or more otherparameters, for example, an angle with respect to the z axis.

The plate 331 may be adjusted by the height adjustment unit 34 toconform to the linear relationship.

As shown in FIG. 3, the plate 331 may be supported by the bracket 332.When the height adjustment unit 34 drives one end away from the bracket332 of the plate 331 to move in a positive direction of the x axis, theplate 331 may not be separated from the bracket 332 completely. Oneunsupported end of the plate 131 may be raised by the height adjustmentunit 34 to tilt the plate 331, such that a surface of the plate 331 mayrise in a positive direction of the z axis.

For example, the height adjustment unit 34 may be installed underneaththe plate 331. The height adjustment unit 34 may include a drive elementconfigured to provide a driving force, a transform element configured totransform a rotation movement to a linear movement, and a transferelement connected to the transform element. The drive element may be,for example, a motor, etc. The transform element may include a leadscrew and a nut. When the motor operates, the lead screw driven by themotor may rotate, and the nut may move in a straight line along the xaxis. Meanwhile, the transfer element may move in a straight linetogether with the nut. The transfer element may drive one end of theplate 331 to rise together, as shown in FIG. 3.

The height adjustment unit 34 may adjust the height of the plate 331 tobe level first, and then continue to raise one end of the plate 331. Thedistance between the bracket 332 and the height adjustment unit 34 inthe z axis is symbolized by a parameter d. The distance of one end ofthe plate 331 away from the bracket 332 raised from the level issymbolized by a parameter h. The distance h may be monitored while theplate rises. A determination may be made as to whether the relationshipamong k, h, and d satisfies the following formula (1). If the formula(1) is satisfied, the plate 331 may have been adjusted in place.Otherwise, the plate 331 the plate 331 may continue to be adjusted as tothe height of the plate 331.

$\begin{matrix}{k = {\frac{h}{d}.}} & (1)\end{matrix}$

There are many ways of monitoring the distance h in real time. Forexample, an encoder may monitor the rotation of the motor in order tomonitor the distance h in real time. As another example, a distancemeasuring unit installed on the floor may monitor the distance h in realtime by monitoring the distance between one end of the plate 331 and thedistance measuring unit. Other devices for measuring the distance h arewithin the scope of the present disclosure and won't be enumerated here.

The height adjustment unit 34 may include a device configured to driveone end of the plate 331 to rise and are not enumerated here. The heightadjustment unit 34 may be installed on the floor, or on the gantry ofthe PET scanner 32. The height adjustment unit 34 may drive the plate331 to move in the x axis and not affect imaging. The method and thelocation of installment of the height adjustment unit 34 are not limitedto those exemplified in the present disclosure.

If the relationship among k, d, and h satisfies the formula (1), theshape of the plate 331 may be kept and a PET scan may be performed. PETimages may be obtained by reconstructing the PET scan data. The changingtrend of the height of the plate 331 in the PET images may conform tothe linear relationship. The relationship may be linear or essentiallylinear. The relationship may represent the changing trend of the heightof the plate 331 in the CT images or topograms. Accordingly, the PET/CTsystem in the some embodiments may obtain CT images and PET images withthe same or essentially the same changing trends of the height of theplate 331. The problem of different changing trends of the height of theplate 331 in different imaging modes may be solved. The fusion ormatching of the images obtained in different imaging modes may besimplified.

FIG. 4 illustrates an exemplary PET/CT system according to someembodiments of the present disclosure. The PET/CT system is similar tothe PET/CT system illustrated in FIG. 3. The PET/CT system in FIG. 4 mayinclude a computing unit 37 configured to compute a distance of theplate 331 that needs to be raised according to the relationshipdetermined by the determining unit 36 described above.

For example, the gradient k may be obtained by the determining unit 36.The distance d between the bracket 332 and the height adjustment unit 34in the z axis may be obtained as described elsewhere in the presentdisclosure. The distance ho of one end of the plate 331 away from thebracket 332 that needs to be raised from the horizontal level may becomputed by the computing unit 37 according to the above formula (1).Then the height adjustment unit 34 may raise the end of the plate 331 byh₀ from the horizontal level. Similar with the description withreference to FIG. 3, the height adjustment unit 34 may drive the plate331 to a horizontal level, and then continue to drive the end of theplate 331 away from the bracket 332 to be raised by ho in the positivedirection of the x axis so that the surface of the plate may fit therelationship described above. A PET scan may be performed. The problemof the different changing trends of the height of the plate in the CTimaging mode and the PET imaging mode may be solved. More descriptionsmay be found elsewhere in the present disclosure. See, for example, FIG.3 and the description thereof.

In the embodiments illustrated in FIG. 3 or FIG. 4, the position of theplate 331 in a CT image may be below the horizontal level, while theposition of the plate 331 in a PET image may be above the horizontallevel. The position error, symbolized by a parameter Δ, may existbetween the CT image and the PET image for a same slice. A changingtrend of a position of the plate in the CT image mode and a changingtrend of the same position of the plate in the PET imaging mode may beessentially the same. Thus the position error Δ between each slice of aCT image and a corresponding portion of a PET image in the x axis may beapproximately equal. As used herein, a portion of a PET image may bereferred to as corresponding to a slice of a CT image when the portionof the PET image and the slice of the CT image represent or depict asame portion of an object that is scanned. The position error Δ may becorrected to compensate the difference of the height of the platebetween the CT imaging mode and the PET imaging mode and to match a CTimage with a corresponding PET image.

FIG. 5 is a diagram illustrating an exemplary PET/CT system according tosome embodiments of the present disclosure. With reference to FIG. 5,the PET/CT system may include a correcting unit 38 configured to correctthe position error of the plate between the CT imaging mode and the PETimaging mode. Position errors in different systems may be different andmay be obtained by experiments.

Experiments may be conducted using a water phantom and loads ofdifferent weights in the PET/CT system. CT images may be obtained byperforming CT scans. The relationship between the heights of the plateand the distances of the plate moving in the axial direction may bedetermined based on CT images. Then the plate may be adjusted so thatthe heights of the plate conform to the relationship. PET images may beobtained by performing a PET scan at a height.

Each position error of the plate between the CT image and the PET imagein the x axis for each slice may be determined, and the mean value ofall position errors may be used as the final position error Δ.

To assess the position error Δ more accurately, the experiment may berepeated for multiple times using a water phantom and loads of differentweights (e.g., wedges of different weights, etc.). For each load,multiple position errors Δ₁, Δ₂, . . . , Δ_(n) may be obtained, in whichn≥1 and n represents the times of the experiments. The times of theexperiments for at least two loads of different weights may be the sameor different. For each load, the mean value of Δ₁, Δ₂ . . . Δ_(n) may bedetermined and used as the final position error Δ.

The position errors Δ for loads of different weights may be obtained byexperiments and may be stored for future use. The position errors Δ maybe acquired directly based on the weight of a patient during a scan whenneeded. In some embodiments, after a PET scan, the correcting unit 38may acquire the position error Δ corresponding to the patient andcorrect the data acquired in the PET scanning. The reconstruction unitof the PET scanner 32 may reconstruct the corrected data to obtain thePET images in which the positions of the plate of PET images may matchthe positions of the plate in the CT images. Because such experimentsmay be performed for a limited number of times, the number of positionerrors that may be obtained by experiments is limited. The weight of apatient may vary widely. When the weight of a patient is not alreadydetermined by experiment, the position error may be obtained byinterpolation or extrapolation.

As illustrated in FIG. 5, the region to be examined is the head of apatient. In this case, the scanning range is short and the positionerror may be minor, for example, about a few millimeters. In someembodiments, the correcting unit 38 may correct the position error asfollows.

The obtaining unit 35 may be configured to obtain images. The images maybe CT images or topograms. The determining unit 36 may be configured todetermine the relationship between the heights of the plate in theimages and the distances of the plate moving in the axial direction. Theheight adjustment unit 34 may be configured to adjust the height of theplate based on the relationship, in order to make the movement of theadjusted plate fit the relationship. The correcting unit 38 may beconfigured to acquire the position error Δ based on the patient and sendit to the controller of the table unit 33 and the height adjustment unit34 such that the entire plate may be lowered by Δ in the x axis. In thiscase, the PET images in which the positions of the plate match thepositions in CT images may be obtained by performing a PET scan. In someembodiments, the distance Δ may be short, and thus the region to beexamined may be still substantially within the center of FOV of the PETscanner 32.

In some embodiments, the PET/CT system may operate as follows. Theobtaining unit 35 may be configured to obtain images. The images may beCT images or topograms. The determining unit 36 may be configured todetermine the relationship between the heights of the plate in theimages and the distances of the plate moving in the axial direction. Therelationship may be linear or approximately linear. The correcting unit38 may be configured to acquire the position error Δ corresponding to apatient and send the position error Δ to the controller of the tableunit 33. The controller may make the plate 331 lower by Δ in the x axis.The height adjustment unit 34 may be configured to adjust the height ofthe plate according to the relationship such that the movement of theadjusted plate (including, for example, the movement along the axialdirection, the height adjustment, and the bending of the plate) may fitthe relationship. In this case, the PET images where the positions ofthe plate match the positions of the plate in the CT images may beobtained by performing a PET scan.

In the PET/CT system, the changing trends of the positions of the platein CT images and in the PET images may be adjusted to be substantiallythe same. Then the position error between a CT image and a PET image maybe corrected based on the experimental data in the PET image in whichthe spatial positions and/or spatial coordinates of the PET image maymatch those in the CT image, thereby facilitating image fusion. In someembodiments an exemplary PET/CT system has been described. It isunderstood that the imaging system may be a single-mode system or amulti-mode system, such as a separated PET system, an MRI system, and soon, in which the difference of the bending of the plate compared withanother imaging system (for example, a CT system) may be compensated.

Merely by way of example, the region to be examined is the head of thepatient. When the scanning range is long, for example, in a whole bodyscan, at least a portion of the plate may bend greatly, and thus theneed to compensate the height of the plate may be great.

Usually, the scan range of the PET unit 32 is about 200 mm in a singlescan. The plate 331 may be moved in the z axis for many times to performmultiple PET scans if a whole body scan is to be performed on a patient.In the case, the height of the plate may be adjusted according to theprocess described elsewhere in the present disclosure, so that thechanging trend of the height of the plate during a PET scan may be thesame or substantially the same as that in a CT scan. Because the heightadjustment unit 34 is installed at a fixed position, the positions ofthe plate 331 in the FOV may be constant for multiple PET scans. Theposition error between the height of the plate during a PET scan and theheight of the plate in a corresponding CT scan may change. Thus the PETscan data may be corrected separately to compensate the difference ofthe heights of the plate between the CT imaging mode and the PET imagingmode, in order to make a CT image and a corresponding PET image match.The correction data may be obtained by experiments conducted in advanceand stored for future use. In some embodiments, the height of the platemay be adjusted to compensate the difference of the heights of the platebetween the CT imaging mode and the PET imaging mode so as to make a CTimage and a corresponding PET image match.

In some embodiments, the scan range of the PET unit 32 may be long. Forexample, a whole body scan may be performed in a single scan.

In the imaging system 30, there is a position 3331 for a CT scan and aposition 3332 for PET scan on the base 333 along the z axis. When thebracket 332 is placed at the position 3331 for CT scan, a patient may beplaced onto or removed from the table unit 33. In some embodiments, theplate may need to exit from the bore of the CT scanner 31 completely toavoid collision with the CT scanner 31 when the plate 331 is moved up ordown. In this case, the distance between one end of the plate 331 closeto CT scanner 31 and the scanning cross-section along the z axis may beat least half of the size of the CT scanner 31 in the z axis, forexample, about 400 mm. The maximum moving distance of the plate may be2100 mm or so. The CT scan may not be performed for the patient if therange of the plate 331 movement is within 400 mm as it needs to leaveenough distance for the plate 331 to slow down. Thus the maximum scanrange of the CT scanner 31 is less than 1700 mm. For a patient who istaller than 1700 mm, the CT scanner 31 may not provide a whole bodyscan.

PET/CT system 40 according to some embodiments of the presentdisclosure, may extend the scan range of the CT scanner without changingthe size of the imaging system.

FIG. 6(a), FIG. 6(b), and FIG. 6(c) are diagrams illustrating differentstates of an exemplary PET/CT system according to some embodiments ofthe present disclosure. With reference to FIG. 6(a), The PET/CT system40 may include a CT scanner 41, a PET scanner 42, and a table unit 43.In some embodiments, the CT scanner 41 and the PET scanner 42 may becoaxial. In some embodiments, the CT scanner 41 and the PET scanner 42may be non-coaxial. The table unit 43 may include a base 433, a bracket432, and a plate 431. The plate 431 may be configured to move relativelyto the bracket 432 along a length direction of the plate 431. The PET/CTsystem of FIG. 6(a) through FIG. 6(c) may include a releasing position4331, a CT scan position 4332, and a PET scan position 4333 on the base433 along the z axis that is parallel to a rotation axis of the CTscanner 41 (i.e., a length direction of the plate 431).

When the bracket 432 is placed at the position 4331, the distance of theplate 431 to move up or down is larger and the plate 431 may move to theposition below the bore of the CT scanner 41 for the patient to beplaced onto or removed from the table unit 43. When the bracket 432 isplaced at the position 4332 (or the position 4333), the distance of theplate 431 to move up or down is shorter than the diameter of the bore ofthe CT scanner 41 (or the PET scanner 42) to avoid collision.

With reference to FIG. 6(a), when the bracket 432 is placed at theposition 4331, the plate 431 may exit from the bore of CT scanner 41completely to avoid collision with CT scanner 41 when the plate 431 ismoved up or down. At this time, the distance of the plate 431 for movingin the x axis is larger, and may be the range from 450 mm to 1000 mm,from 500 mm to 1000 mm, from 550 mm to 950 mm, or from 550 mm to 945 mm,wherein the distance may be the distance from the floor in the x axis.The plate 431 may move to a position about 500 mm above the floor, whichis convenient for a short patient to get or be placed onto or removedfrom the table unit 43.

Optionally, when the bracket 432 is placed at the position 4331, if theplate 431 moves in the x axis with a displacement relative to thebracket 432, the alarm may be triggered; optionally, when the bracket432 is placed at the position 4331, the plate 431 may be unable to movein the x axis with a displacement relative to the bracket 432;optionally, when the bracket 432 is placed at the position 4331, if thedistance from the plate 431 to the floor is outside a given range, theplate 431 may move up or down in the x axis but not in the z axis; ifthe distance from the plate 431 to the floor is within the given range,the plate 431 may move in the z axis; optionally, when the bracket 432is placed at the position 4331, the plate 431 may move up or down in thex axis but not in the z axis without a displacement relative to thebracket 432. It may improve the safety to avoid the collision due tomisoperation at the position 4331.

With reference to FIG. 6(b), when the CT scan is to be performed for apatient, the bracket 432 may be placed at the position 4332, and thedistance between one end of the plate 431 close to CT scanner 41 and thescanning cross-section in the z axis is short. The speed of the plate431, referred to as the scan speed, may be low when a CT scan isperformed in the CT scanner 41. In FIG. 6(b), the distance between oneend of the plate 431 close to CT scanner 41 and the scanningcross-section in the z axis is long enough to allow the plate 431 toaccelerate to the scan speed. The distance between one end of the plate431 close to CT scanner 41 and the scanning cross-section in the z axismay be in the range from 20 mm to 200 mm, from 20 mm to 150 mm, from 20mm to 100 mm, or from 20 mm to 50 mm, etc.

Merely by way of example, the maximum distance for the plate 431 to movein the z axis is about 2100 mm; the maximum distance is assumed to be2160 mm; the distance between one end of the plate 431 close to CTscanner 41 and the scanning cross-section in the z axis is 50 mm whenthe bracket 432 is placed at the position 4332. That is, the distancefor the plate 431 to accelerate from 0 to the scan speed is 50 mm. Thedistance for the plate 431 to slow down from the scan speed to 0 is 50mm when the scan ends. If the scan range is 2000 mm, the distance forthe plate 431 to move corresponding to the scan range is 50 mm+2000mm+50 mm=2100 mm, which is less than the maximum distance 2160 mm. Sothe PET/CT system 40 may extend the scan range of the CT scanner 41compared with the PET/CT system 30 in FIG. 3 to FIG. 5.

The maximum scan range of the CT scanner 41 may be determined by themaximum distance for the plate to move, the scan speed and theacceleration of the plate, or the like, or a combination thereof.Suppose the maximum distance for the plate 431 to move is L, thedistance for the plate 431 to accelerate from 0 to the scan speed is S₁and the distance for the plate 431 to slow down from the scan speed to 0is S₂, and the maximum scan range of the CT scanner 41 is:

L-S₁-S₂  (2)

In some embodiments, suppose the maximum distance for the plate 431 tomove is 2160 mm and the distance for the plate 431 to accelerate ordecelerate is 50 mm, the maximum scan range of the CT scanner 41 is 2160mm−50 mm−50 mm=2060 mm. If the maximum distance for plate 431 to move is2200 mm, the maximum scan range of the CT scanner 41 is 2100 mm. Themaximum scan range of the CT scanner 41 may also be other values, forexample, 1700 mm. Without increasing the size of the table unit 43, themaximum scan range of the CT scanner 41 is from 1700 mm to 2100 mm, 2060mm, 2000 mm, 1960 mm, or 1900 mm, and so the CT scanner 41 maysubstantially perform a whole body scan for many patients.

When the bracket 432 at the position 4332, the distance for the plate431 to move in the x axis is shorter and may be the range from 700 mm to1000 mm, from 750mm to 1000 mm, from 800 mm to 950 mm, or from 820 mm to945 mm. As used herein, the distance for the plate 431 to move in the xaxis is the distance from the floor in the x axis. The motion range ofthe plate 431 in the x axis may be limited. When the plate 431 moves inthe positive direction of the x axis, the patient may need to beprotected from collision with the CT scanner 41; when the plate 431moves in the negative direction of the x axis, the plate 431 may need tobe protected from collision with the CT scanner 41.

With reference to FIG. 6(c), when the PET scan is to be performed for apatient, the bracket 432 is placed at the position 4333 and the wholebody of the patient is in the FOV of the PET scanner 42 such that thePET scanner 42 may perform a whole body scan in a single scan. The FOVmay be related to the size of the PET scanner 42 in the z axis and maybe the range from 1700 mm to 2000 mm, from 1800 mm to 2000 mm, or from1900 mm to 2000 mm, etc.

When the bracket 432 is at the position 4333, the distance for the plate431 to move in the x axis may be the same as that during the CT scanningor not, provided that the plate 431 or the patient does not collide withthe PET scanner 42.

In some embodiments, the distance between one side of the CT scanner 41and the scanning cross-section in the z axis may be about 400 mm long,and the FOV of the PET scanner 42 may be about 2000 mm long. Thedistance between the scanning cross-section and the center of the FOV isabout 1400 mm. If the distance between position 4332 and position 4333is 1400 mm, the structure and size of the table unit 43 may need to bechanged, which may cause an increase in not only the size of the imagingsystem but also the cost. So the distance between position 4332 andposition 4333 may be different from the distance between the scanningcross-section and the center of FOV of the PET scanner 42.

Compared with the embodiments in FIG. 3 to FIG. 5 in which the distancebetween one end of the plate 331 close to CT scanner 31 and the scanningcross-section is about 400 mm when the bracket 332 is placed at theposition 3331, the distance between one end of the plate 431 close to CTscanner 41 and the scanning cross-section is only about 50 mm when thebracket 432 is placed at the position 4332. If the maximum distance forthe plate to move in FIG. 6(a), FIG. 6(b), or FIG. 6(c) is the same asthat in FIG. 3 to FIG. 5, the longer distance for the plate 431 of thetable unit 43 to move may be used for the CT scan in the embodimentsillustrated in FIG. 6(a), FIG. 6(b), and FIG. 6(c). That is, theembodiments illustrated in FIG. 6(a), FIG. 6(b), and FIG. 6(c) mayextend the scan range of the CT scanner 41 without increasing the sizeof the table unit 43.

When the scan range is longer, one unsupported end of the plate 431 maybend with the movement of the plate 431 in the z axis during a CT scan.The farther the plate 431 moves in the z axis, the more seriously theplate 431 bends. The unsupported end of the plate 431 may also bendduring a PET scan. From the description of FIG. 1 and FIG. 2, the trendsof the bending of the plate in a CT image and a corresponding PET imagemay be opposite. Thus, the bending of the plate may be compensated bycombining the embodiments described with reference to FIG. 6(a), FIG.6(b), and FIG. 6(c) with the embodiments described with reference toFIG. 3 to FIG. 5, in order to compensate the difference of the bendingof the plate between the CT imaging mode and the PET imaging mode.

For example, the PET/CT system 40 may include a height adjustment unit44 configured to adjust the height of the plate 431 based on the heightof the plate 431 at the scanning cross-section during the CT scan sothat the changing trend of the height of the adjusted plate 431 during aPET scan is consistent with the changing trend of the height of theplate during the CT scan. To compensate the difference of the bendingbetween the CT imaging mode and the PET imaging mode, the heightadjustment unit 44 may be controlled to drive the plate 431. The PET/CTsystem 40 may further include an obtaining unit 45 and a determiningunit 46.

The obtaining unit 45 may be configured to obtain images. The images maybe CT images or topograms.

The determining unit 46 may be configured to determine the relationshipbetween the heights of the plate in the images and the distances of theplate moving in the axial direction. In some embodiments, therelationship may be linear or substantially linear. In some embodiments,the relationship may be non-linear.

The height adjustment unit 44 may be configured to adjust the height ofthe plate based on the relationship to make the movement of the adjustedplate (including, for example, the movement of the plate along the axialdirection, the height adjustment, the bending of the plate) fit therelationship. In this case, PET scan data may be obtained by a PET scan.PET images may be obtained by reconstructing the PET scan data. Thechanging trend of the height of the plate 431 in a PET image may beconsistent with the changing trend of the height of the plate in a CTimage. There may be a position error of the plate between the CT imageand the corresponding PET image for a same slice. The position error maybe corrected to compensate the difference of the height of the platebetween the CT imaging mode and the PET imaging mode and to make the CTimage and the corresponding PET image match.

In some embodiments, the PET/CT system 40 may further include acorrecting unit 48 configured to correct the position error of the plateduring a PET scan compared to a CT scan.

The position error with respect to loads of different weights may beobtained by experiments and stored. The position error may be acquireddirectly based on the weight of a patient when needed. Specifically,after a PET scan, the correcting unit 48 may obtain the position errorrelating to the patient and correct data acquired in the PET scanning.The reconstruction unit of the PET scanner 42 may reconstruct thecorrected data to obtain the PET images in which the positions of theplate may match the positions of the plate in CT images. The matchingmay be obtained by performing a PET scan after the entire plate 431 isadjusted for the position error.

More descriptions may be found elsewhere in the present disclosure. See,for example, the description with reference to FIG. 3 to FIG. 5.

FIG. 7 is a flowchart illustrating an imaging process according to someembodiments of the present disclosure.

In step 701, images may be obtained.

The images may be CT images or topograms. In some embodiments, CT imagesare provided merely for illustration purposes, and not intended to limitthe scope of the present disclosure.

In step 702, a relationship between the heights of the plate in theimages and the distances of the plate moving in the axial direction maybe determined. In some embodiments, the relationship may be linear orsubstantially linear. In some embodiments, the relationship may benon-linear.

In step 703, the plate may be adjusted according to the relationship, inorder to make the movement of the adjusted plate fitting the linearrelationship.

The plate may be adjusted according to the linear relationshipdetermined in step 702, in order to make the surface of the plate(including, for example, the movement of the plate along the axialdirection, the height adjustment, the bending of the plate) fit therelationship. The distance may be monitored when the plate rises toassess the movement of the plate based on the relationship. The distanceby which the plate needs to rise based on the relationship may bedetermined in advance and then one end of the plate may be raised tomake the movement of the plate fit the relationship.

In step 704, an imaging scan may be performed.

In this case, a PET scan may be performed. The problem that the changingtrend of the height of the plate in the CT imaging mode is differentfrom that in the PET imaging mode may be solved. PET images may beobtained by reconstructing the PET scan data, in which the changingtrend of the height of the plate in the PET images may be consistentwith that in the CT images. Image fusion that matches the imagesobtained in different imaging modes may be simplified.

In some embodiments, there may be a position error of the plate betweenthe PET images and the CT images. The position error may be corrected tocompensate the difference of the height of the plate between the CTimaging mode and the PET imaging mode and to make a CT image and acorresponding PET image match. In some embodiments, the imaging processmay further include step 705.

In step 705, the scan data may be corrected.

The position error may be corrected by lowering the plate directly, asshown in FIG. 8. More descriptions may be found elsewhere in the presentdisclosure. See, for example, the description with reference to FIG. 3to FIG. 6.

FIG. 8 is a flowchart illustrating an imaging process according to someembodiments of the present disclosure.

In step 801, the images may be obtained.

The images may be CT images or topograms. In some embodiments, CT imagesare provided merely for illustration purposes, and not intended to limitthe scope of the present disclosure.

In step 802, the relationship between the heights of the plate in theimages and the distances of the plate moving in the axial direction maybe determined. In some embodiments, the relationship may be linear orsubstantially linear. In some embodiments, the relationship may benon-linear.

In step 803, the plate may be adjusted according to the relationship, inorder to make the movement of the adjusted plate fit the relationship.The movement of the plate may include, for example, the movement of theplate along the axial direction, the height adjustment, the bending ofthe plate.

In step 804, the position error may be obtained.

In step 805, the plate may be adjusted according to the position errorto make the height of the adjusted plate constant in various images.

In step 806, an imaging scan may be performed.

In some embodiments, the position error in step 804 may be obtainedbefore the step 801, which is a variation within the scope of thepresent disclosure.

More description may be found elsewhere in the present disclosure. See,for example, the description with reference to FIG. 3 to FIG. 6.

Having thus described the basic concepts, it may be rather apparent tothose skilled in the art after reading this detailed disclosure that theforegoing detailed disclosure is intended to be presented by way ofexample only and is not limiting. Various alterations, improvements, andmodifications may occur and are intended to those skilled in the art,though not expressly stated herein. These alterations, improvements, andmodifications are intended to be suggested by this disclosure, and arewithin the spirit and scope of the exemplary embodiments of thisdisclosure.

Moreover, certain terminology has been used to describe embodiments ofthe present disclosure. For example, the terms “one embodiment,” “anembodiment,” and/or “some embodiments” mean that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Therefore, it is emphasized and should be appreciated that two or morereferences to “an embodiment” or “one embodiment” or “an alternativeembodiment” in various portions of this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures or characteristics may be combined assuitable in one or more embodiments of the present disclosure.

Further, it will be appreciated by one skilled in the art, aspects ofthe present disclosure may be illustrated and described herein in any ofa number of patentable classes or context including any new and usefulprocess, machine, manufacture, or composition of matter, or any new anduseful improvement thereof. Accordingly, aspects of the presentdisclosure may be implemented entirely hardware, entirely software(including firmware, resident software, micro-code, etc.) or combiningsoftware and hardware implementation that may all generally be referredto herein as a “block,” “module,” “engine,” “unit,” “component,” or“system.” Furthermore, aspects of the present disclosure may take theform of a computer program product embodied in one or more computerreadable media having computer readable program code embodied thereon.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including electro-magnetic, optical, or thelike, or any suitable combination thereof. A computer readable signalmedium may be any computer readable medium that is not a computerreadable storage medium and that may communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus, or device. Program code embodied on acomputer readable signal medium may be transmitted using any appropriatemedium, including wireless, wireline, optical fiber cable, RF, or thelike, or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB. NET,Python or the like, conventional procedural programming languages, suchas the “C” programming language, Visual Basic, Fortran 2003, Perl, COBOL2002, PHP, ABAP, dynamic programming languages such as Python, Ruby andGroovy, or other programming languages. The program code may executeentirely on the operator's computer, partly on the operator's computer,as a stand-alone software package, partly on the operator's computer andpartly on a remote computer or entirely on the remote computer orserver. In the latter scenario, the remote computer may be connected tothe operator's computer through any type of network, including a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider) or in a cloud computing environment oroffered as a service such as a Software as a Service (SaaS).

Furthermore, the recited order of processing elements or sequences, orthe use of numbers, letters, or other designations therefore, is notintended to limit the claimed processes and methods to any order exceptas may be specified in the claims. Although the above disclosurediscusses through various examples what is currently considered to be avariety of useful embodiments of the disclosure, it is to be understoodthat such detail is solely for that purpose, and that the appendedclaims are not limited to the disclosed embodiments, but, on thecontrary, are intended to cover modifications and equivalentarrangements that are within the spirit and scope of the disclosedembodiments. For example, although the implementation of variouscomponents described above may be embodied in a hardware device, it mayalso be implemented as a software only solution—e.g., an installation onan existing server or mobile device.

Similarly, it should be appreciated that in the foregoing description ofembodiments of the present disclosure, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure aiding in theunderstanding of one or more of the various inventive embodiments. Thismethod of disclosure, however, is not to be interpreted as reflecting anintention that the claimed subject matter requires more features thanare expressly recited in each claim. Rather, inventive embodiments liein less than all features of a single foregoing disclosed embodiment.

In some embodiments, the numbers expressing quantities of ingredients,properties, and so forth, used to describe and claim certain embodimentsof the application are to be understood as being modified in someinstances by the term “about,” “approximate,” or “substantially.” Forexample, “about,” “approximate,” or “substantially” may indicate ±20%variation of the value it describes, unless otherwise stated.Accordingly, in some embodiments, the numerical parameters set forth inthe written description and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by aparticular embodiment. In some embodiments, the numerical parametersshould be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof some embodiments of the application are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspracticable.

Each of the patents, patent applications, publications of patentapplications, and other material, such as articles, books,specifications, publications, documents, things, and/or the like,referenced herein is hereby incorporated herein by this reference in itsentirety for all purposes, excepting any prosecution file historyassociated with same, any of same that is inconsistent with or inconflict with the present document, or any of same that may have alimiting affect as to the broadest scope of the claims now or laterassociated with the present document. By way of example, should there beany inconsistency or conflict between the description, definition,and/or the use of a term associated with any of the incorporatedmaterial and that associated with the present document, the description,definition, and/or the use of the term in the present document shallprevail.

In closing, it is to be understood that the embodiments of theapplication disclosed herein are illustrative of the principles of theembodiments of the application. Other modifications that may be employedmay be within the scope of the application. Thus, by way of example, butnot of limitation, alternative configurations of the embodiments of theapplication may be utilized in accordance with the teachings herein.Accordingly, embodiments of the present application are not limited tothat precisely as shown and described.

What is claimed is:
 1. A method comprising: obtaining images by scanninga subject placed on a plate of a table in a CT imaging mode; determininga linear relationship between height of the plate in the images anddistance of the plate moving in a length direction of the plate;adjusting the height of the plate according to the linear relationshipsuch that a movement of the adjusted plate fits the linear relationship;obtaining a position error of the plate between the CT imaging mode anda PET imaging mode; adjusting, according to the position error, theheight of the plate in the PET imaging mode; and performing, in the PETimaging mode, a PET scan for the subject placed on the adjusted plate.2. The method of claim 1, wherein the adjusting the height of an end ofthe plate according to the linear relationship such that a movement ofthe adjusted plate fits the linear relationship includes: determining araised height according to the linear relationship and a measureddistance of the plate moving in the length direction of the plate; andadjusting the height of the end of the plate based on the determinedraised height.
 3. The method of claim 1, wherein the obtaining aposition error of the plate between the CT imaging mode and a PETimaging mode includes: obtaining the position error from experimentalposition error data with a water phantom and loads of different weights,wherein the obtained position error corresponds to the load of theweight of the subject.
 4. The method of claim 3, wherein the adjusting,according to the position error, the height of the plate in the PETimaging mode includes: lowering the height of the plate by the obtainedposition error.
 5. The method of claim 1, wherein the images are CTimages or topograms.
 6. A PET/CT system comprising: a CT scannerconfigured to perform CT scanning in accordance with a CT imaging mode;a PET scanner configured to perform PET scanning in accordance with PETimaging mode; a table including a base, a bracket, and a plate movablerelative to the bracket; at least one computer readable medium includingexecutable instructions; and at least one processor in communicationwith the executable instructions, wherein when executing the executableinstructions, the at least one processor is configured to cause thesystem to perform operations including: obtaining images by scanning asubject placed on the plate of the table in the CT imaging mode;determining a linear relationship between height of the plate in theimages and distance of the plate moving in a length direction of theplate; adjusting the height of the plate according to the linearrelationship such that a movement of the adjusted plate fits the linearrelationship; obtaining a position error of the plate between the CTimaging mode and the PET imaging mode; adjusting, according to theposition error, the height of the plate in the PET imaging mode; andperforming, in the PET imaging mode, the PET scan for the subject placedon the adjusted plate.
 7. The PET/CT system of claim 6, wherein theadjusting the height of an end of the plate according to the linearrelationship such that a movement of the adjusted plate fits the linearrelationship includes: determining a raised height according to thelinear relationship and a measured distance of the plate moving in thelength direction of the plate; and adjusting the height of the end ofthe plate based on the determined raised height.
 8. The PET/CT system ofclaim 6, wherein the obtaining a position error of the plate between theCT imaging mode and a PET imaging mode includes: obtaining the positionerror from experimental position error data with a water phantom andloads of different weights, wherein the obtained position errorcorresponds to the load of the weight of the subject.
 9. The PET/CTsystem of claim 8, wherein the adjusting, according to the positionerror, the height of the plate in the PET imaging mode includes:lowering the height of the plate by the obtained position error.
 10. ThePET/CT system of claim 6, wherein the images are CT images or topograms.11. The PET/CT system of claim 6, wherein the base includes a releasingposition, a CT scan position and a PET scan position.
 12. The PCT/CTsystem of claim 11, wherein a distance of the plate to move up or downwhen the bracket is placed at the releasing position of the base islarger than a distance of the plate to move up or down when the bracketis placed at the CT scan position of the base.
 13. The PCT/CT system ofclaim 11, wherein when the bracket is placed at the PET scan position ofthe base, the plate is movable for a distance from a floor on which thetable is placed the same as the distance for the plate to move from thefloor when the bracket is placed at the CT scan position.
 14. The PCT/CTsystem of claim 11, wherein the plate is movable for a distance from afloor on which the table is placed in a range from 500 mm to 1000 mmwhen the bracket is placed at the releasing position of the base. 15.The PCT/CT system of claim 11, wherein the plate is movable for adistance from the floor in a range from 750 mm to 1000 mm when thebracket is placed at the CT scan position.
 16. A method comprising:obtaining images by scanning a subject placed on a plate of a table in aCT imaging mode; determining a linear relationship between height of theplate in the images and distance of the plate moving in a lengthdirection of the plate; adjusting the height of an end of the plateaccording to the linear relationship such that a movement of theadjusted plate fits the linear relationship; and performing, in a PETimaging mode, a PET scan for the subject placed on the adjusted plate.17. The method of claim 16, further comprising: correcting, based on aposition error between the CT imaging mode and the PET imaging mode,scan data acquired in the PET scanning.
 18. The method of claim 17,further comprising: reconstructing a PET image based on the correctedscan data.
 19. The method of claim 17, wherein the position error isobtained from experimental position error data with a water phantom andloads of different weights, the obtained position error corresponding tothe load of the weight of the subject.
 20. The method of claim 16,wherein the images are CT images or topograms.